Steering columns manufactured by the Saginaw Division, General Motors Corporation, Saginaw, Mich., 48605 and used on current model Pontiac Grand Prix, Oldsmobile Cutlass Supreme, and Buick Regal vehicles have anti-theft steering shaft locks of the type including a slotted keeper on the steering shaft and a modular bolt assembly on a fixed part of the steering column. The modular bolt assembly is subassembled separate from the steering column and includes a generally rectangular support tube adapted for rigid attachment to the fixed part of the steering column, a slidable bolt in the support tube, a plastic retainer closing an open end of the support tube, and a spring between the retainer and the bolt urging the latter to an extended position projecting into a slot in the keeper and restricting rotation of the steering shaft. The retainer has integral flexible hooks which hold the retainer on the support tube against the bias of the spring but which are difficult to install and which are prone to looseness and loss during transport of the modular assemblies to steering column final assembly. A modular bolt assembly according to this invention incorporates a structurally more simple plastic retainer which is easier to assemble and which has superior retention and stability relative to the aforesaid hooked retainer.